This week 'Core Web Vitals' section (within Google's Search Console tool) started to show an alert about the increase of the First Input Delay (FID) in thousands of my webpages, which previously had no problem with FID. Most of the URLs I haved in Google passed from green to orange in 7 days. The error is: FID issue: longer than 100ms (mobile)
If I check any of the suggested URLs with PageSpeed Insights, web.dev, or Chrome Lighthouse, I do not see any warning about First Input Delay (FID). And the 'Web Vitals' extension for Chrome claims that the FID for any of the suggested URLs is always bellow 10 ms.
So, what's wrong with my web pages? Is there any tool which helps me to measure the FID correctly and find the origin of the problems? I'm worried about this issue. Some weeks ago, I lost 20% of my valid URLs because of an increment of very slow pages (marked in red by Core Web Vitals).
I do not use jQuery, and most of the JavaScript is written inline within the code. I just do a few call for external JavaScript libraries:
- Google's 'analytics.js': I do it in the original way that Google suggests
- Google's 'adsbygoogle.js': I call it when user starts to scroll down through
var a=document.getElementsByTagName("script")[0];
var b=document.createElement("script");
b.type="text/javascript",b.async=!0,b.src="https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js";
a.parentNode.insertBefore(b,a);
- Leaflet (to build maps): I call it when user starts to scroll down through
var c = document.createElement('script');
c.src = "https://cdnjs.cloudflare.com/ajax/libs/leaflet/1.4.0/leaflet.js";
document.head.appendChild(c);